This project aims to characterize the nature, distribution, and ecologic importance of viruses carried by spiroplasmas. Recent studies of the rod-shaped virus SpV1 show single-hit infection kinetics, an adsorption constant of 2.55 to the negative ninth power cubic cm/min, a latent period of 60 to 90 min, and delayed host cell death unrelated to virus-induced lysis. Virus infectivity survives non-ionic detergents, Genetron, nucleases, heterologous viral antiserum, and drying; but is sensitive to other degergents, chloroform, ether (to some extent), homospecfic antiserum, pH is less than 7 or greater than 9, and temperatures greater than 60 C or (if prolonged) 4 C. Eight new isolates of SpV1 from spiroplasmas from bee, corn, and citrus diseases showed host range differences but no evidence of host modification or restriction. All were equally sensitive to specific antiserum raised against the original isolate from a bee spiroplasma. Viral DNA by electron microscopy appears to be duplex and linear but its size, precise conformation, and other characteristics are under continuing study.